Ethylene alkylation resulting in alkylate with high proportion of 2,3-dimethylbutane

ABSTRACT

AN IMPROVED METHOD FOR THE PREPARATION OF 2,3-DIMETHYLBUTANE ADMIXED WITH A BRANCHED C8 ALKYLATE MIXTURE BY SULFRIC ACID ALKYLATION IS PROVIDED IN A TWO-STAGE PROCESS WHEREIN ISOBUTYLENE ARE CO-DEMERIZED IN THE PRESENCE OF ISOBUTANE AND SULFRIC ACID UNDER REACTION CONDITIONS WHICH FAVOR THE FORMATION OF 3,3-DIMETHYL-1-BUTYL SULFATE, AND THEREAFTER THE SAID 3,3-DIMETHYL-1-BUTYL SULFATE IS REACTED WITH THE ISOBUTANE UNDER CONDITION WHICH FAVOR THE FORMATION OF 2,3-DIMETHYLBUTANE. THIS PROCESS IS ADVANTAGEOUS IN THAT IT PERMITS THE INCORPORATION OF ETHYLENE INTO A SULFRIC ACID ALKYLATION REACTION WITHOUT THE FORMATION OF LARGE AMOUNTS OF UNWANTED ETHYL SULFATE.

United States Patent O 3,754,052 ETHYLENE ALKYLATION RESULTING INALKYLATE WITH HIGH PROPORTION OF 2,3-DHVIETHYLBUTANE David M. Hoffman,Wilmington, Del., and Abraham Schneider, Lower Merion, Pa., assignors toSun Research and Development Co., Philadelphia, Pa.

No Drawing. Filed Jan. 14, 1972, Ser. No. 217,954 Int. Cl. C07c 3/54 US.Cl. 260683.61 16 Claims ABSTRACT OF THE DISCLOSURE An improved methodfor the preparation of 2,3-dimethylbutane admixed with a branched Calkylate mixture by sulfuric acid alkylation is provided in a two-stageprocess wherein isobutylene and ethylene are co-dimerized in thepresence of isobutane and sulfuric acid under reaction conditions whichfavor the formation of 3,3-dirnethyl-l-butyl sulfate, and thereafter thesaid 3,3-dimethyl-l-butyl sulfate is reacted with the isobutane underconditions which favor the formation of 2,3-dimethylbutane. This processis advantageous in that it permits the incorporation of ethylene into asulfuric acid alkylation reaction Without the formation of large amountsof unwanted ethyl sulfate.

BACKGROUND OF THE INVENTION This invention relates to the incorporationof ethylene into a sulfuric acid catalyzed alkylation process to form abranched C alkylate mixture containing a high proportion of2,3-dimethylbutane. More particularly, this invention relates to amethod of first co-dimerizing ethylene and isobutene in the presence ofisobutane and sulfuric acid catalyst to form 3,3-dimethyl-1-butylsulfate, and thereafter reacting said sulfate with isobutane underalkylation conditions to form a product containing substantial amountsof 2,3-dimethylbutane. This latter product is, of course, especiallyuseful as a motor fuel component.

U.'S. Pat. No. 2,660,602 teaches a method of preparing branched primarysulfate esters by combining ethylene with another olefin in the presenceof sulfuric acid catalyst. Included in this teaching is the reaction ofethylene with isobutene to form 3,3-dimethyl-l-butyl sulfate. However,nowhere in this patent is there the teaching or suggestion that thissulfate compound may advantageously be employed as an intermediate inthe alkylation of isobutane to form 2,3-dimethylbutane.

U.S. Pat. 2,381,041 teaches that alkyl esters of polybasic mineralacids, such as sulfuric acid, can be reacted with branched chainparaffins to form alkylation products of the isoparafiin. This referencedoes not, however, teach the use of 3,3-dimethyl-1-butyl sulfate in thealkylation of isobutane to yield 2,3-dimethylbutane.

More significantly, neither of the above references teaches alone or incombination a solution to the longstanding problem of how to incorporateethylene into a sulfuric acid-catalyzed alkylation reaction withoutforming substantial amounts of undesired ethyl sulfate, which lattercompound cannot be utilized to alkylate an isoparaflin.

SUMMARY OF THE INVENTION It has now been found, in accordance with thepresent invention, that ethylene may be employed in a sulfuric acidcatalyzed alkylation reaction with an isoparaffin such as isobutanewithout forming large amounts of ethyl sulfate by-products. Such aprocess is highly advantageous in that ethyl sulfate, when formed inaccordance with conventional processes cannot further react with theisoparaflin to alkylate the same, and thus large amounts of ethylene arelost.

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The process of the present invention achieves the incorporation ofethylene into an alkylation reaction while at the same timesubstantially avoiding formation of unreactive ethyl sulfate byvproviding a novel two-stage alkylation reaction. In the first stageethyelne is co-dimerized with a higher molecular weight olefin such asisobutene in the presence of sulfuric acid and the isoparaifin to bealkylated,, e.g. isobutane, under reaction conditions which favor theformation of a stable alkyl sulfate ester of the olefin co-dimer ratherthan the formation of ethyl sulfate. Thereafter, in the second stage thesaid alkyl sulfate ester of the co-dimer is reacted with the isoparafiinunder conditions favoring hydride ion transfer of the co-dimer sulfuricacid ester with the isoparaflin, followed by subsequent self-alkylationof the isoparaifin. The product formed is predominantly a branched Calkylated hydrocarbon fuel containing high proportions of2,3-dimethylbutane.

DESCRIPTION OF THE INVENTION The process will now be described withparticular reference to the use of ethylene, isobutene and isobutane toform an alkylate containing a high proportion of 2,3- dimethylbutane(hereinafter 2,3-DMB) In the first stage isobutylene is desirablyintroduced slowly into an emulsion of sulfuric acid and isobutane attemperatures of from about 10 to 12 C., and preferably not more thanabout 0 C., in a reactor that is pressured with ethylene, preferably ata pressure of about 60 to p.s.i. The product is chiefly3,3-dimethyl-l-butyl sulfate, a stable, recoverable sulfate ester of theethyleneisobutylene co-dimer. Under these reaction conditions onlyslight amounts of ethyl sulfate formation or alkylation of the isobutanetake place.

The mole ratio of ethylene to isobutylene in this stage may be in therange of 1:1 to 100:1 and is preferably 5:1 to 25:1. It will beunderstood that the ratio of the two olefins is more critical than thatof the isobutane, which is merely acting as a diluent in this firststage to prevent oligomerization. Thus, it is only necessary that theisobutane be present in volume amounts sufiicient for that purpose,preferably, although not essentially, in the range of from 2:1 to 25:1based on total volume of olefin employed.

In this first stage, the sulfuric acid employed as the catalyst shouldhave a concentration of about to weight percent. The volume of suchcatalyst present in the first stage reaction medium should be equal tothat of the total volume of hydrocarbons present, although the ratio ofacid volume to hydrocarbon may range from about 0.25:1 to 10:1.

The co-dimerization reaction is generally rapid, and in any event thereaction is substantially completed in about 1 to 15 minutes after theaddition of the olefin is complete.

For purposes of this process, it is not essential that the co-dimersulfate ester be separated and recovered before the second stagealkylation. Instead, the temperature of the total reaction mixturecomprising some unreacted ethylene, an acid phase containing principallysaid sulfate ester, and a hydrocarbon phase containing principallyisobutane and additional unreacted ethylene may be elevated, followingventing of the ethylene, to about 25 C. and preferably from about 35 to50 C., whereupon said sulfate ester will alkylate with said isobutane toform the desired product. Alternatively, and more desirably, however,the acid phase containing said sulfate ester is first separated from thehydrocarbon phase and thereafter reacted with fresh isobutane at theaforesaid elevated temperature.

In the second stage the mole ratio of co-dimer sulfuric acid ester toisobutane reactant should desirably be in the range of 1:1. to 1:25 andpreferably 1:4 to 1:10. The

initial sulfuric acid catalyst concentration should be maintained at thesame concentration and volume as in the first stage, if necessary by theintroduction of small amounts of additional acid. The time necessary tocomplete the alkylation will range from 10 to 120 minutes, and generallyabout 60 minutes, depending principally upon the temperature employed.

-In both stages, as in conventional alkylation processes, vigorousagitation of the acid and hydrocarbon phases should be maintainedthroughout the reaction. Any known agitation means may be employed.

As aforestated, the product comprises 2,3-dimethylbutane admixed with aC alkylate mixture, although small amounts of C to C7 branchedhydrocarbons may also be recovered, as for example methylpentanes,methylhexanes and the like.

In a further embodiment of this process, it has been found that otherolefins can be substituted for isobutylene. In such a substitution thestable sulfate ester formed in the first stage is a mixture of olefin/ethylene co-dirner sulfate ester and 3,3-dimethyl-1-butyl sulfate whichis formed from the t-butyl cation (by hydride extraction from isobutane)and ethylene. In addition to 2,3-dimethylbutane, the final productcontains large amounts of isopentane when the olefin is propylene;considerable amounts of 3-methylpentane when the olefin is butene-l orbutene-2; and large amounts of 2,3-dimethylbutane when the olefin is2,3-dimethylbutene. 'In the last case, the 2,3-dimethylbutane is formedboth by initial hydride extraction in the first stage and by reaction ofthe t-butyl cation/ethylene co-dimer sulfate ester with isobutane in thesecond stage.

Example 1 Into a l-liter stirred Parr reactor equipped with coolingcoils was placed 200 cc. of 96 percent H 80 2.0 cc. of n-octane(internal standard) and 150 cc. of isobutane. The contents of thereactor were cooled to -8 to 9 C. by circulating cold acetone throughthe cooling coils and the pressure of the reactor brought to 80 p.s.i.with ethylene and maintained between 60 to 80 p.s.i. with ethylenethroughout the reaction. *Isobutylene (21.5 g.) dissolved in 100 cc. ofisobutane was added to the vapor space through a needle over a period of25 minutes. Following the butylene addition the ethylene pressure wasvented and a sample of the hydrocarbon layer was taken for VPC analysis.The temperature of the reactor was quickly raised to 35 C. bycirculating warm water through the coils and the reaction continued for2 hours with samples of the hydrocarbon being taken at l-hour intervals.These samples had the following analysis:

Isobutylene-isobutane alkylatloign tha pesence of 60-80 p.s.i. ofethylene o Time at 35 0. (111111.)

Alkylate yield (wt. percent based 011104)- 28 239 396 What is claimedis:

1. A process for the preparation of a branched-chain hydrocarbon motorfuel which includes a high proportion of 2,3-dimethylbutane, saidprocess comprising contacting ethylene with isobutylene in the presenceof isobutane and concentrated sulfuric acid catalyst at a temperature offrom about 10 to 12 C. to form a reaction mixture comprising unreactedethylene, an acid phase containing 3,3-dimethyl-l-buty1 acid sulfateester, and a hydrocarbon phase containing isobutane, removing unreactedethylene from said reaction mixture and thereafter raising thetemperature of said reaction mixture to at least about 25 C. in order toalkylate said sulfate ester with said isobutane, and recovering apredominantly branched C alkylate fuel containing a high proportion of2,3- dimethylbutane.

2. The process according to claim 1 wherein the ethylene is maintainedin contact with the isobutylene at a pressure of from about 60 to p.s.i.

3. The process according to claim 1 wherein the mole ratio of ethyleneto isobutylene is from about 1:1 to :1.

4. The process according to claim 1 wherein acid catalyst is present inthe reaction medium in a ratio of about 0.25:1 to 10:1 by volume basedon the volume of hydrocarbon present.

5. The process according to claim 1 wherein the volume ratio ofisobutane solvent to total volume of olefin is from about 2:1 to 25-: 1.

6. The process according to claim 1 wherein the mole ratio of sulfateester to isobutane reactant is from about 1:1 to 1:25.

7. The process according to claim 1 wherein the contact time between thesulfate ester and the isobutane reactant is between about 10 andminutes.

8. A process for preparing a branched-chain hydrocarbon motor fuel whichincludes a high proportion of 2,3-dimethylbutane, said process comprisescontacting ethylene with an olefin selected from the group consisting ofpropylene, butcne-l, butenc-Z, and 2,3-dimcthylbutene in the presence ofisobutane and concentrated sulfuric acid catalyst at a temperature offrom about ---10 to 12 C. to form a reaction mixture comprisingunreacted ethylene, an acid phase containing a mixture of a codimer acidsulfate ester and 3,3-dimethyl-1-butyl acid sulfate ester, and ahydrocarbon phase containing isobutane and unreacted ethylene, saidco-dimer in said sulfate ester comprising said ethylene co-dimcrizedwith said olefin, removing unreacted ethylene, and thereafter raisingthe temperature of the reaction mixture to at least about 25 C. in orderto alkylate said sulfate esters with said isobutane, and recovering apredominantly branched C alkylate fuel containing a high proportion of2,3- dimethylbutane.

9. The process according to claim 8 wherein the ethylene is maintainedin contact with the olefin at a pressure of from about 60 to 80 p.s.i.

10. The process according to claim 8 wherein the mole ratio of ethyleneto olefin is from about 1:1 to 100:1.

11. The process according to claim 8 wherein acid catalyst is present inthe reaction medium in a ratio of about 0.25:1 to 10:1 by volume basedon the volume of hydrocarbon present.

12. The process according to claim 8 wherein the volume ratio ofisobutane solvent to total volume of olefin is from about 2:1 to 25:1.

13. The process according to claim 8 wherein the mole ratio of sulfateesters to olefin reactant is from about 1:1 to 1:25.

14. The process according to claim 8 wherein the contact time betweenthe sulfate esters and the isobutane reactant is between about 10 and120 minutes.

15. A process for the preparation of a branchedchain hydrocarbon motorfuel which includes high a proportion of 2,3-dimethylbutane, saidprocess comprising contacting ethylene with isobutylene in the presenceof isobutane and concentrated sulfuric acid catalyst at a temperature offrom about -10 to 12 C. to form a reaction mixture comprising unreactedethylene, an acid phase containing 3,3-dimethyl-l-butyl acid sulfateester, and a hydrocarbon phase containing isobutane, removing unreactedethylene from said reaction mixture, phase separating the acid phasecontaining said acid sulfate ester from the hydrocarbon phase,thereafter reacting said acid phase with isobutane at a temperature ofat least about 25 C. in order to alkylate said sulfate ester with saidisobutane, and recovering a predominantly branched C alkylate fuelcontaining a high proportion of 2,3-di methylbutane.

16. A process for preparing a branched-chain hydrocarbon motor fuelwhich includes a high proportion of 2,3-dimethylbutane, said processcomprises contacting ethylene with an olefin selected from the groupconsisting of propylene, butene 1, butene 2, and 2,3 dimethylbutene inthe presence of isobutane and concentrated sulfuric acid catalyst at atemperature of from about 10 to 12 C. to form a reaction mixturecomprising unreacted ethylene, an acid phase containin a mixture of aco-dimer acid sulfate ester and 3,3-dimethyll-butyl acid sulfate ester,and a hydrocarbon phase containing isobutane and unreacted ethylene,said co-dimer with said olefin, removing unreacted ethylene from saidreaction mixture, phase separating the acid phase containing said acidsulfate ester from the hydrocarbon phase, thereafter reacting said acidphase with isobutane, at a temperature of at least about 25 C. in orderto alkylate said sulfate esters with said isobutane, and recovering apredominantly branched C alkylate fuel containing a high proportion of2,3-dimethylbutane.

References Cited UNITED STATES PATENTS 2,314,333 3/1943 Francis260-68361 2,319,209 5/1943 Carmody 260-68359 2,660,602 11/1953 Wiese260-460 DELBERT E. GANTZ, Primary Examiner G. I. CRASANAKIS, AssistantExaminer US. Cl. X.R. 260-460

